1. Technical Field
This invention relates in general to flexible cables and in particular to devices for isolating and reinforcing a flexible cable having set bend corners or hinge areas.
2. Background Art
Devices which require the use of flexible cables such as flat ribbon cable are well known in the art. These devices typically have a stationary element and a dynamic element which moves relative to the stationary element between extended and retracted positions. Flexible cables are needed to provide input/output signals and/or power signals by extending between and interconnecting the two elements. Since the extended position is further away from the stationary portion than the retracted position, the flexible cable must be provided with enough cable length to reach both positions. Thus, when the dynamic portion is in the retracted position, the excess cable length must be accommodated. This is typically accomplished by bending or folding the cable along at least one bend radius.
However, as the dynamic element is repeatedly cycled between the extended and retracted positions, the flexible cable undergoes incessant flexure. The flexible cable experiences bending stresses at its bend radii and will eventually fatigue over time. The process is accelerated if the flexible cable is creased, or if the bend radii are limited to specific portions of the cable.
One type of prior art device, disclosed in U.S. Pat. No. 5,669,749, describes a movable, flexible ribbon cable with a support band assembly. In this device, the dynamic element flexes or bends the cable throughout its length. Thus, although this is a dynamic application, the hinge region of the cable is in continuous motion as the dynamic element of the device moves between the extended and retracted positions. The hinge region is not isolated or fixed as described above.
In U.S. Pat. No. 5,175,398, another type of prior art device uses a cable that is interconnected between a keyboard and the CPU. The cable has predefined hinge regions which are isolated by shrink tubing or the like to minimize the stresses exerted at the bend radii of the cable. Although this design is workable, it is a noncontinuous application which is generally not expected to exceed 50,000 flex cycles. In contrast, applications involving automated moving elements may require a cable to endure more than one million flex cycles. Moreover, the shrink tubing places a discontinuity on the hinge regions which causes higher stress concentrations.
Therefore, it is a feature of the present invention to provide an apparatus for isolating and reinforcing a flexible cable having set or predefined hinge regions.
It is another feature of the present invention to provide such an apparatus for extending the flex life of the cable while minimizing the bend radii of the hinge regions.